We will examine the neural control of cardio-respiratory function, using long-term recording of single neurons in defined areas of the forebrain, pons, and medulla. Neuronal discharge will be studied during spontaneous sleep-waking cycling and during challenges to the respiratory and cardiovascular systems. The cardio-respiratory measures that will be examined include cardiac and respiratory rates and their variability, cardiac arrhythmias, blood pressure, and ventilatory patterns (Ti, Te, Vt). Challenges to the cardiovascular and respiratory systems will include transient elevation of blood pressure, atrial pacing, tracheal occlusion, hypercapnia, hypoxia, vasotomy, and stimulation of forebrain and pontine sites. Cardiovascular and respiratory variability during each state will be assessed with time series and autocorrelation techniques. Activity of neurons in forebrain and brain stem areas will be examined with point process display and correlation procedures during normal sleep-waking conditions and during the experimental challenges. Interactions between forebrain and brain stem areas will be studied by examining the shared discharge of neurons with peristimulus histograms, cross-correlation procedures, and time series analysis techniques.